The use of cryosurgical probes for necrotizing lesions is well known. When using a probe to freeze wet tissue, such as in the mouth or the cervix, cryoadhesion results from a thin layer of ice forming between the tissue and the probe surface, adhering to each, and bonding them together. In devices which use the expansion of warm gas (Joule-Thompson principle) to achieve cooling, it has been known to circulate warm gas in order to create a thaw cycle, after freezing. However, the extent of freezing which is achievable utilizing warm gases (such as nitrous oxide) is inadequate in many instances.
Cryogenic devices which spray liquid nitrogen, substantially in the liquid phase, directly on inner surfaces of closed probes and vent the gas therefrom, are far more effective for necrotizing lesions than the devices which use warm gas cycles. However, there is no warm gas to circulate in order to provide a thaw to break the cryoadhesion. In most modern cryosurgery, hand-held units utilizing dewars of on the order of a half liter or less are generally employed. These devices typically use a variety of probes which are detachably affixed thereto as required. This presents the problem of providing a thaw cycle to a detachable probe.
When using liquid nitrogen or other cryogenic gases, the degree of freezing is quite extensive, thereby requiring significant heat in order to create an adequate thaw to break the cryoadhesion. However, in many applications, the probe may be inserted within a body cavity, thereby making it imperative that parts of the body which are not to be necrotized are not damaged either by freezing or by burning. This presents the problem of providing adequate heat to relieve the cryoadhesion while at the same time not creating additional hazard from the heat.